The control and flow of surface water, such as rain water or storm water, is important in preventing the build up of surface water adjacent to the foundations of buildings or other structures, and in other areas such as playing fields, golf courses, landscaped decks, gardens and the like. Roof gardens are becoming increasingly popular both to “green” buildings and make them more environmentally friendly, and also to provide recreational spaces. The use of drainage cells in roof gardens is critical in allowing excess water to escape quickly from the roof garden to drainage outlets. This reduces the potential for leakage of water through roofs, and also helps prevent load issues due to the weight of water, growth media and the like on top of a building's roof.
A typical drainage cell (often known as a dimpled drainage sheet) is formed from an extruded sheet of plastic in which is formed an array of protruding frusto-conical dimples. A layer of geo-textile is adhered to the base of the frusto-conical sections of the drainage cell. The cells are placed with the base of the frusto-conical sections and the geo-textiles facing upwards. The opposite face, or base, of the cell typically lies on a sheet of waterproof membrane or like when used in a roof garden application.
However, the problem with the existing drainage cells is that flow tends to be inhibited by the volume of the conical dimples occupying the space beneath the geo-textile layer. More significantly, the geo-textile tends to sag due to the weight of soil or other growth medium lying on top of the geo-textile layer. This tends to block or partially block the spaces between the conical dimples, thus impeding water flow and slowing the rate of water flow through the drainage cell. The problem of sagging geo-textile tends to increase as the drainage cell and geo-textile age.
The present invention aims to provide an improved drainage cell which addresses some of the problems of prior art drainage cells discussed above.
Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.